1 Field of the Invention
The present invention relates to an optical pick-up for a high density optical recording medium, and more particularly, to a micro-mirror device for controlling a position of beam and detecting an optical signal, and an optical pick-up system of the same.
2 Background of the Related Art
The recent rapid development of the multimedia technology is made possible owing to development of faster, and low cost large sized information storage devices. The improvement of PC performance, the rapid spreading of data communication, such as the internet, and the debut of VOD (Video On Demand) and the high definition TVs strongly demand for large sized information storage media which can process a large amount of data, inclusive of moving pictures and audio signals, further. Though there are magnetic storages which are made to meet such demands by increasing a storage density and capacity of existing HDD (Hard Disk Drive), it is known that it is very difficult to realize a magnetic storage with a density over 10 giga bytes per square inch due to a physical limitation of recording density.
Starting from popularization of compact disks, the optical information storage is settled as a major supplementary storage for PC, and is being developed to put DVD (Digital Versatile Disc) systems, which can be applicable to a wide multimedia environment, into practical use. Particularly, the optical information storage is advantageous in that it has a fast response speed and pick-up of non-contact type, and especially, a data density as high as a range of a wavelength of writing/reading laser beam can be available. However, the higher density of data implies a reduction of a track pitch, a distance between data bits or tracks, as much as a range of a wavelength of the writing/reading laser beam. Therefore, an optical system which can control a position of the writing/reading laser beam to direct the laser beam to a position of the track pitch accurately is an important task of the high density optical information storage. The micro optical system emerged owing to micromachining technology is assumed to be a technology which can realize control of the micro laser beam displacement mentioned before. Not only the optical information storage field, but also the example of the DMD (Digital Mirror Display) of the Texas Instrument, a new concept display, are examples of application of a micro mirror array, a micro optical device. And, the application of the micro optical device implemented by the micromachining is in a wide spreading trend, such as a paper on study for a laser beam scanner for reading a bar code by using polycrystalline silicon surface micromachining (J. Microeletromech. Syst. vol. 7, no. 1, pp. 27-37, 1998). FIG. 1 illustrates a related art optical pick up, schematically.
Referring to FIG. 1, the related art optical pickup is provided with a laser diode 21, a light source, for emitting a laser beam, which reaches to a specific data bit position on a disk 27 surface via optical system elements arranged properly, such as a collimating lens or collimator 22, converging lenses 24, 26 and 28, beam splitter 23, and a mirror 30 on a 45xc2x0 sloped surface of a submount 25, reflected at the disk surface 27 again, and comes to a photodiode 29 for detecting an optical signal, thereby determining a digital code(0 or 1) of the specific data. The mirror 30 makes a fine movement so that the laser beam finds the data at the specific position on the optical disk, which is controlled by a position controller, such as a voice coil actuator.
However, the related art optical pickup has the following problems. First, the related art optical system is, not only restricted merely to positioning of an incident light, such as positioning of the light source, variation of a reflection angle, and the like, but also poor in accuracy of the positioning of the light.
Second, the numerous components in the related art optical system causes the optical system large and complicated, to deteriorate mass productivity and have a high cost.
Accordingly, the present invention is directed to a micro-mirror device and an optical pick-up system of the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a micro-mirror device and an optical pick-up system of the same, in which a positioning function and an optical signal detecting function are integrated, for reducing components of the optical system, and simplifying the optical system.
Other object of the present invention is to provide a micro-mirror device and an optical pick-up system of the same, in which a micro drive mirror is used for improving accuracy of positioning of an incident light.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the micro-mirror device includes a mirror driver on a substrate, a beam splitting mirror part movable in an up or down direction in parallel by the mirror driver for fine adjusting of a position of a beam, reflecting the beam, and transmitting a portion of the beam, and an optical detector under the beam splitting mirror part for sensing the beam passed through the beam splitting mirror part, wherein the optical detector is either a pn junction photodiode, or a pin junction photodiode.
The mirror driver includes a piezoelectric actuator adapted to deform according to an external control signal, a connecting part connected between the beam splitting mirror part and the piezoelectric actuator for transferring the deformation of the piezoelectric actuator to the beam splitting mirror part for shifting the beam splitting mirror part, and a controller for controlling the deformation of the piezoelectric actuator, and the piezoelectric actuator includes a spacer formed at an edge of the micro-mirror device to a thickness, a cantilever spaced a distance from a surface of the substrate, and a piezoelectric body formed on or in the cantilever.
The beam splitting mirror part includes a mirror for reflecting a portion of an incident light and transmitting the other portion of the light, and a transparent supporter formed beneath the mirror for supporting the mirror, wherein the mirror is either a grating halfmirror or a Fresnel lens.
In other aspect of the present invention, there is provided an optical pick up system of a micro-mirror device including a light source module for emitting a light, a first and a second focusing parts for focusing the light emitted from the light source module onto a surface of an optical recording medium, and the micro-mirror device between the first and second focusing parts for fine adjustment of a position of the light incident through the first focusing part, reflecting to the optical recording medium through the second focusing part, sensing the light re-reflected at the optical recording medium, and converting into an electrical signal.
Thus, by integrating/packing optical components, such as the mirror, the optical signal detecting photodiode, and the beam positioning device, a micro optical system can be fabricated, and by simplifying an optical system assembly process, a mass productivity is increased and a production cost is saved, and by using the parallel driven micro actuator, beam positioning can be made to a nanometer level.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.